A plastic tank must be operated
at atmospheric pressure (air must enter and exit the tank as it is filled and
emptied). All of our above-ground tanks come with a vented manway. If 3” or 4”
outlets are used or rapid dispensing is possible, an additional vent fitting
should be considered.
compatibility chart for appropriate fitting and gasket material.
The fitting must be above the
bottom knuckle radius of the tank (the curve which is formed inside the tank,
blending the side wall with the bottom). On rectangular tanks, the fitting must
not be installed too close to the adjacent wall. Good gasket compression is
necessary for a leak-proof seal.
chart for maximum fitting size.
To drain a tank below the outlet
fitting location, you may use a siphon drain
Mark the position of center
point of the fitting on the outside of the tank with a grease pencil or marker.
Cut a hole in the tank using a
hole saw of the proper diameter. The proper diameter is found by measuring the outside
thread diameter of the fitting body. It is advisable to cut a hole in a
scrap of plastic or wood and test fit the bulkhead through the hole. It should
pass into the hole but should not have more than a maximum of 1/16th inch of
Hint: If access to the inside of tank is limited (manway too
small to reach into the tank or the tank is too big to move easily around), use
a string as a guide for the bulkhead fitting. Cut a length of string 3 times
the distance from the tank manway to the fitting hole. Run the string from
manway through the fitting hole. You may have to fish the string through
the fitting hole by using a stick to pull the string through the hole
(duct tape on the end of the stick will help the process). Put the gasket
on the fitting body and pass the string through the body. The gasket side
of body should be facing the fitting hole. Tie a pencil or stick behind the
fitting. Pull string from fitting hole to lead the fitting. When fitting is
through the hole, attach nut and release the string.
The nut must now be tightened
(hand tightened only). If you have installed a siphon tube, be certain that is
facing the correct direction.
The tank will expand and
contract. Flexible connections must be used between tank fitting and rigid pipe
Water test your tank to check